I. Field of the Invention
This invention relates to threaded closures for drum containers to prevent the escape of materials from within the drum and, in particular, to a closure having a structural and material composition capable of rupturing when exposed to elevated temperatures and pressures to vent the drum container.
II. Description of the Prior Art
Closures are utilized in drum containers to selectively enclose materials within the container. Such closures can include spout closures which facilitate pouring of materials from the container and threaded closures which must be removed from the container opening to access material. However, this same sealing property can result in a pressure build-up when the containers are exposed to elevated temperatures such as in a fire. Accordingly, it is desirable for a closure to seal the container for transport of materials but vent a build-up of pressure within the container to prevent explosive rupturing of the drum container.
The prior known rupturable closures typically include a second wall or membrane which breaks under predetermined pressures. The scores or grooves control the rupture configuration which also determines the pressures needed to rupture the closure. These same scores can cause the closure to inadvertently rupture resulting in leakage of material from the container. What is needed is an integral closure which ruptures after deforming due to extreme temperatures.
The present invention overcomes the disadvantages of the prior known closures by providing a threaded closure for a drum container which incorporates a center portion deformable under extreme temperatures and pressure to rupture and vent pressure build-up from the container.
The venting drum closure of the present invention is adapted to be threadably seated within an opening of a drum container to present escape of materials within the container. The closure includes an annular sidewall having threads on the exterior surface. Extending outwardly at substantially a right angle to the sidewall is an annular flange to facilitate handling of the closure and provide for a sealing surface against the container. A base wall extends across the closure within the annular sidewall. The base wall includes an annular outer portion of a first material thickness and an inner or central portion of a second, thinner material thickness. The material composition and thickness of the central portion causes the center to distort under predetermined temperatures and pressures eventually rupturing to vent internal pressures within the drum container. Conversely, the center portion is sufficiently stable to prevent inadvertent rupture and leakage past the closure. The base wall includes additional structure to maintain the integrity of the closure during normal operation. An annular flange depends downwardly from the underside of the base wall substantially encircling the thinner central portion. Formed on the topside of the base wall are a plurality of lugs peripherally spaced along the side wall. In a preferred embodiment, the lugs have a substantially trapezoidal configuration so as not to extend over the central portion of the base wall. Nevertheless, the lugs provide added support to the base wall to maintain integrity during normal use. Accordingly, the closure of the present invention has sufficient structural integrity to meet requirements for transportation of materials yet will vent potentially explosive pressures from the drum container when subjected to elevated temperatures and pressures.